Stamper for optical disk, method for manufacturing optical disk, and optical disk

ABSTRACT

This invention relates to a stamper for optical disc and a method for manufacturing an optical disc by using this stamper. A photoresist is applied to a substrate ( 2 ) and this photoresist is exposed, developed and then transferred to form a disc master which has a recess/protrusion pattern formed on its one side. The one side of the disc master ( 20 ) is etched to narrow the width of a protruding part constituting the recess/protrusion pattern, and the recess/protrusion pattern of the disc master ( 20 ) with the reduced width of the protruding part is transferred to form a stamper ( 30 ). The recess/protrusion pattern provided on the stamper ( 30 ) is transferred to form a predetermined pattern on a substrate of an optical disc.

TECHNICAL FIELD

[0001] This invention relates to a stamper for optical disc whichtransfers a predetermined pattern to an optical disc substrate, a methodfor manufacturing an optical disc using this stamper, and an opticaldisc manufactured by this manufacturing method.

BACKGROUND ART

[0002] There is an optical disc which enables recording of informationsignals at a higher recording density than on such optical discs as CD(compact disc) and DVD (digital versatile disk). An optical disc of thistype enables recording of information signals at a higher recordingdensity than on CD or DVD by using a light beam having a wavelength ofapproximately 400 nm, which is shorter than in the case of CD or DVD,for recording or reproducing information signals, and using a numericalaperture (NA) of an objective lens of approximately 0.85, which islarger than in the case of CD or DVD.

[0003] For example, the optical disc which enables recording ofinformation signals at a higher recording density than on CD or DVD hasa predetermined pattern consisting of lands and grooves formed on oneside of a disc substrate, a reflection layer provided for reflecting alight beam onto the predetermined pattern, a signal recording layer madeof a phase change material or the like and provided on the reflectionlayer, and a light-transmitting layer provided on the signal recordinglayer, and recording or reproduction of information signals is carriedout by casting a light beam from the light-transmitting layer side.

[0004] Meanwhile, with respect to optical discs, it has been known thata better recording/reproducing characteristic can be realized whenrecording information signals to a land, which is a protruding part,than when recording information signals to a groove, which is a recesspart. Therefore, on the optical disc with a higher recording density ofinformation signals, information signals are recorded to lands bycasting a light beam from the optical transmitting layer side, which isopposite to the substrate.

[0005] When manufacturing the optical disc with a higher recordingdensity, first, a photoresist is applied on one side of a glass masterboard and it is exposed and developed to form a recess/protrusionpattern. Nickel-plating or silver-plating is performed thereon tomanufacture a disc master. Then, a mother master is manufactured bytransferring the recess/protrusion pattern formed on the disc master.This mother master is used as a stamper for forming a predeterminedpattern on a disc substrate. Specifically, when manufacturing CD or DVD,a stamper is formed by further transferring the recess/protrusionpattern of the mother, whereas for this optical disc, the mother mastercan be used as a stamper and a recess part for recording informationsignal, that is, a land, can be formed on the light-transmitting layerside. On the substrate on which the recess/protrusion pattern istransferred from the stamper as a mother master and thus a predeterminedpattern is formed, a reflection layer, a signal recording layer and alight-transmitting layer are sequentially stacked on the side where thepredetermined pattern is formed.

[0006] Meanwhile, in the case where the ratio of the width of aprotruding part to the width of a recess part is set to 1:1 when forminga recess/protrusion pattern on the disc master in order to form a landand a groove on the disc substrate and thus a disc substrate on whichthe ratio of the width of the land to the width of the groove is 1:1 isformed, if a reflection layer and a signal recording layer are formed onthe disc substrate, the ratio of the width of the land to the width ofthe groove will not be 1:1 and the land will become wider than thegroove.

[0007] For example, if a predetermined pattern having a recess part witha depth of 20 nm and a land with a width of 0.16 μm, which is half thetrack pitch of 0.32 μm, is formed on the disc substrate and a signalrecording layer is formed thereon, the width of the land will be largerthan the width of the groove by approximately 0.02 μm.

[0008] To enable reproduction of an information signal-recordableoptical disc in a reproducing device for a reproduction-only opticaldisc having a pit string formed on a disc substrate, the land must bemade narrower than the groove to reduce the quantity of reflection of alight beam. This is because the reproducing device for thereproduction-only disc reads out information signals by detecting thereflectivity of a light beam cast onto the optical disc but cannotdetect information signals if the reflectivity is too high.

[0009] Therefore, in the information signal-recordable optical disc fromwhich reproduction can be carried out by the reproducing device for thereproduction-only optical disc, the width of the land need be less than50% of the track pitch when the signal recording layer is formed. Tosatisfy this condition, the width of the recess part for forming theland of the stamper must be less than at least 50%, preferably less than45% of the track pitch, in consideration of the thickness of thereflection layer and the signal recording layer. However, a cuttingmachine for exposing a photoresist applied on a glass master board whenforming a disc master which is commercially available at present uses alight beam with a minimum wavelength of 257 nm or 266 nm. Even when thediameter of a beam spot is minimized, it is difficult to reduce thewidth of the track to less than 45% ofthe track pitch. For example, whenthe track pitch is 0.32 μm and the depth of the recess part is 20 nm,the width of the recess part is 45% to 50% of the track pitch at best.Moreover, when the width of the recess part is decreased toapproximately 45% to 50% of the track pitch, the surface of the stamperwill be rough and causes diffuse reflection when reflecting a lightbeam. Therefore, a good recording/reproducing characteristic cannot beobtained. To realize a good recording/reproducing characteristic, thewidth of the recess part must be approximately 45% to 65% of the trackpitch.

DISCLOSURE OF THE INVENTION

[0010] Thus, it is an object of the present invention to provide a newstamper for optical disc, a method for manufacturing an optical disc,and an optical which enable prevention of diffuse reflection of a lightbeam on a reflection layer by forming the surface of a substrate withoutany minute recesses and protrusions and thus enable improvement inrecording/reproducing characteristic.

[0011] It is another object of the present invention to provide astamper for optical disc, a method for manufacturing an optical disc,and an optical disc which enable reduction in quantity of reflection ofa light beam by making the width of a land narrower than the width of agroove in the state where a signal recording layer is provided, and thusenable reproduction in a reproducing device for a reproduction-onlyoptical disc.

[0012] It is a further object of the present invention to provide astamper for optical disc and a method for manufacturing an optical discwhich enable manufacture of an optical disc on which the width of a landis narrower than the width of a groove in the state where a signalrecording layer is provided, by using an existing cutting machine.

[0013] In order to achieve the foregoing objects, a stamper for opticaldisc according to the present invention has a recess/protrusion patternformed on one side thereof, the recess/protrusion pattern being fortransferring a predetermined pattern to a substrate of an optical disc.The one side has surface roughness (Ra) of 0.4 nm or less for forming aflat surface of the substrate without any recesses and protrusions. Inthis stamper, at least the width of a recess part for forming a land maybe less than 50% of a track pitch so that the width of the land isnarrower than the width of a groove in the state where a reflectionlayer and a signal recording layer are formed on the substrate. In thiscase, for example, the track pitch is 0.35 μm or less. Since the stamperis flatly formed with surface roughness (Ra) of 0.4 nm or less, there isa risk of sticking to the substrate when releasing. Thus, in thestamper, the recess/protrusion pattern may be provided at least in oneof non-signal recording areas on an inner circumferential side and anouter circumferential side in addition to a signal recording area, thusimproving its mold release characteristic.

[0014] A method for manufacturing an optical disc according to thepresent invention comprises the steps of: applying a photoresist to asubstrate, exposing and developing the photoresist to form arecess/protrusion pattern on one side, and forming a disc master onwhich a transfer pattern is formed on the basis of the substrate;etching one side of the disc master and thus reducing the width of aprotruding part constituting the transfer pattern; further transferringthe transfer pattern of the disc master with the reduced width of theprotruding part and thus forming a stamper; and transferring therecess/protrusion pattern provided on the stamper and thus forming apredetermined pattern on a substrate of an optical disc. That is, inthis manufacturing method, since the roughness on the surface iseliminated by etching the surface of the disc master, exposure can becarried out by using, for example, an existing cutting machine,irrespective of the wavelength of a light beam for exposure.

[0015] Moreover, in order to achieve the foregoing objects, an opticaldisc according to the present invention has a reflection layer and aprotection layer stacked on a substrate which has a predeterminedrecess/protrusion pattern provided on its one side, and the substratehas the predetermined pattern formed thereon as a recess/protrusionpattern is transferred thereto by a stamper having surface roughness(Ra) of 0.4 nm or less. Therefore, the surface of the substrate is flatand also the reflection layer provided thereon is flatly formed. Thisprevents diffuse reflection of a light beam incident from alight-transmitting layer.

[0016] The other objects of the present invention and specificadvantages provided by the present invention will be clarified furtherfrom the following description of an embodiment with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a cross-sectional view showing essential parts of anoptical disc to which the present invention is applied.

[0018]FIG. 2 is a perspective view showing essential parts of theoptical disc shown in FIG. 1.

[0019]FIG. 3 is a cross-sectional view showing essential parts of a discmaster used in the method of the present invention.

[0020]FIG. 4 is a cross-sectional view showing essential parts toexplain the state where disc master shown in FIG. 3 is being etched.

[0021]FIG. 5 is a cross-sectional view showing essential parts of thedisc master on which etching is performed.

[0022]FIG. 6 is a cross-sectional view showing essential parts of astamper (mother master) manufactured on the basis of the disc master.

[0023]FIG. 7 is a cross-sectional view showing essential parts of asubstrate on which a predetermined pattern is transferred by using thestamper.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] A stamper, a method for manufacturing an optical disc and anoptical to which the present invention is applied will now be describedwith reference to the drawings.

[0025] First, an optical disc 1 to which the present invention isapplied will be described with reference to the drawings. As shown inFIGS. 1 and 2, this optical disc 1 has a substrate 2 having a land 2 aand a groove 2 b formed on its one side, a reflection layer 3 providedon the side of the substrate 2 where the land 2 a and the groove 2 b areformed, a signal recording layer 4 provided on the reflection layer 3,and a light-transmitting layer 5 provided on the signal recording layer4. This optical disc 1 is adapted for recording information signals tothe signal recording layer 4 by casing a light beam thereto from theside of the light-transmitting layer 5. The optical disc 1 has adiameter of 12 cm and a recording capacity of approximately 25gigabytes.

[0026] The substrate 2 is a synthetic resin substrate molded by aninjection-molding machine. It is molded with a thickness which enablessecure transfer of a recess/protrusion pattern of a stamper, forexample, 1.1 mm. Since a light beam is cast onto this substrate 2 fromthe side of the light-transmitting layer 5 unlike the conventional CDand DVD, the light transmittancy of the substrate 2 is not necessarilyrequired.

[0027] On one side of the substrate 2, the land 2 a as a protruding partand the groove 2 b as a recess part are formed in a vortex-like manner.These land 2 a and groove 2 b are formed as the recess/protrusionpattern provided on the stamper is transferred to the substrate 2 whenmolding the substrate 2. On the sidewall of the groove 2 b,wobble-modulated address information is recorded. The groove 2 b isformed with its depth D being λ/10 to λ/12 of the wavelength (λ) of alight beam, specifically, approximately 20 nm. The land 2 a and thegroove 2 b are formed in such a manner that a track pitch TP isapproximately 0.32 μm. In order to make the width of the land 2 a on thesignal recording layer 4 less than 50% ofthe track pitch TP, the widthW₁ of the land 2 a is caused to be less than 50% of the track pitch TP,preferably less than 45% of the track pitch TP, in consideration of thethickness of the reflection layer 3 and the signal recording layer 4.

[0028] The surface of the side of the substrate 2 where the land 2 a andthe groove 2 b are formed is formed by a stamper with surface roughness(Ra) of 0.4 nm or less and therefore is made flatter than in the case ofan ordinary substrate. Therefore, in the optical disc 1, the reflectionlayer 3 applied on the substrate 2 securely reflects a light beam castthereto without causing diffuse reflection, thus improving therecording/reproducing characteristic.

[0029] On one side of such a substrate 2, the land 2 a and the groove 2b are formed not only in a signal recording area in which informationsignals are recorded, but also in at least an inner circumferentialnon-signal recording area provided on the inner circumferential side ofthe signal recording area or an outer circumferential non-signalrecording area provided on the outer circumferential side of the signalrecording area. Since the one side of the substrate 2 is flattened, itsmold release characteristic with respect to the stamper is lowered.Thus, the stamper has the recess/protrusion pattern at least in thenon-signal recording area on the inner circumferential side or the outercircumferential side as well as the signal recording area, thusimproving the mold release characteristic with respect to the substrate2. The spacing between the land 2 and the groove 2 b provided in thenon-signal recording area is 0.1 mm or less. This because if the spacingbetween the land 2 a and the groove 2 b is larger than 0.1 mm, thesynthetic resin for molding the substrate 2 sticks to the stamper side.

[0030] On the one side of the substrate 2 where the land 2 a and thegroove 2 b are formed, the reflection layer 3 for reflecting an incidentlight beam is formed. This reflection layer 3 is formed by evaporating ametal such as aluminum on the one side of the substrate 2.

[0031] On the reflection layer 3, the signal recording layer 4 made of aphase change material is formed. This signal recording layer 4 is formedto a thickness T₁ of 200 nm. In the state where the signal recordinglayer 4 is formed, the land 2 a has a width W₂ which is less than 50% ofthe track pitch TP. The signal recording layer 4 may also be made of anorganic dye material, a dielectric substance or the like, as well as thephase change material.

[0032] On the signal recording layer 4, the light-transmitting layer 5for transmitting a light beam emitted from an optical pickup is formed.For example, this light-transmitting layer 5 is formed by attaching alight-transmitting polymer sheet onto the signal recording layer 4 witha pressure-sensitive adhesive. Such a light-transmitting layer 5 isformed to a thickness T₂ of, for example, 0.1 mm.

[0033] In the optical disc 1 constituted as described above, as a lightbeam with a wavelength of approximately 400 nm cast from the side of thelight-transmitting layer 5 is condensed by using an objective lens 10with a numerical aperture (NA) of 0.85, information signals are recordedto the signal recording layer 4 or information signals recorded on thesignal recording layer 4 are read out. This optical disc 1 is rotated ata CLV (constant linear velocity) by a disc rotational driving mechanism.

[0034] In the optical disc 1 according to the present invention, sincethe one side of the substrate 2 is flatly formed, also the reflectionlayer 3 can be flatly formed. As a result, diffuse reflection of a lightbeam incident from the light-transmitting layer 5 can be prevented andthe recording/reproducing characteristic can be improved. Since thewidth of the land 2 a of the optical disc 1 is less than 50% of thetrack pitch in the state where the signal recording layer 4 is formedand the quantity of reflection of the light beam is restrained,reproduction of this optical disc 1 in a reproducing device for areproduction-only optical disc on which information signals are recordedin the form of pits is made possible and cross talk noise can bereduced.

[0035] A method for manufacturing the optical disc 1 as described abovewill now be described.

[0036] Manufacture of the stamper for forming the predetermined patternon the substrate 2 will first described. First, a glass master board isprepared. After a side of the glass master board to which a photoresistis to be applied is polished and flattened, the photoresist is applied,for example, to a thickness of approximately 20 nm in accordance withthe depth of the groove 2 b. Then, the photoresist is dried. Heattreatment is performed on the glass master board to which thephotoresist is applied, and the glass master board is stabilized.

[0037] Next, the photoresist applied to the glass master board is cut,that is, exposed, to a predetermined pattern by a cutting machine. Thecutting machine exposes the photoresist to the predetermined pattern byusing a light beam with a wavelength of 266 nm and an energy density of0.052 mJ/m². In this case, the cutting machine rotates the glass masterboard at a CLV and exposes the photoresist on the basis of thewobble-modulated address information. The exposed area is an area to bethe land 2 of the substrate 2.

[0038] Then, as the photoresist exposed on the basis of thepredetermined pattern is developed, the exposed part is removed. Thus, arecess/protrusion pattern is formed on the glass master board. Byelectroless plating of nickel or the like, a disc master 20 shown inFIG. 3 is formed from the glass master board on which therecess/protrusion pattern is formed.

[0039] As shown in FIG. 3, a protruding part 20 a and a recess part 20 bare continuously provided on this disc master 20. The recess part 20 bis formed to a depth D of, for example, 20 nm. The track pitch TP is0.32 μm and the protruding part 20 a is formed to a width W₃ of 0.16 μm,which is half the track pitch TP.

[0040] Then, this disc master 20 is etched until the width W₃ of theprotruding part 20 a is reduced to less than 45% of the track pitch TP,as shown in FIG. 4. The etching in this case is dry etching. Forexample, the disc master 20 is set in a chamber which is made vacuum to8.0×10⁻³ Pa by a rotary pump or a turbo pump, and oxygen or argon issupplied at such a flow rate as to realize 1×10⁰ Pa. Then, etching iscarried out for 60 seconds with an RF power of 150 W. As this etching iscarried out once, the width W₄ of the protruding part 20 a is reduced by0.013 μm, as shown in FIG. 5. By carrying out this etching twice, thewidth W₄ of the protruding part 20 a can be reduced to approximately0.134 μm, with the track pitch TP of 0.32 μm. By this etching, the sidewhere the photoresist is provided is flattened.

[0041] A mother master is manufactured on the basis of the disc master20 on which etching is performed as described above. The mother masterbecomes a stamper 30 for transferring a predetermined pattern to thesubstrate 2, as shown in FIG. 6. Since this stamper 30 is manufacturedon the basis of the disc master 20 with its surface etched, the stamper30 has surface roughness (Ra) of 0.4 nm or less. In this stamper 30, thetrack pitch TP is 0.32 μm and a recess part 30 b for forming the land 2a on the substrate 2 has a width W₅ of 0.134 μm.

[0042] Specifically, in this stamper 30, the width W₅ of the recess part30 b is caused to be not less than 30% and less than 50% of the trackpitch TP so that the width W₂ of the land 2 a of the substrate 2 in thecase where the signal recording layer 4 is formed is less than 50% ofthe track pitch TP in order to enable reproduction of the optical disc 1in a reproducing device for a reproduction-only optical disc. Thepurpose of causing the width W₅ of the recess part 30 b to be not lessthan 30% of the track pitch TP is to secure a necessary quantity ofreflection in order to enable reproduction in a reproducing device for areproduction-only optical disc. The width W₅ of the recess part 30 b isset within the range of not less than 30% to less than 50% of the trackpitch TP in consideration of the thickness of the reflection layer 3 andthe signal recording layer 4 formed on the substrate 2.

[0043] The stamper 30 is set in a metal mola and the substrate 2 with athickness of approximately 1.1 mm is formed by injection-molding asshown in FIG. 7. The W₁ of the land 2 a formed on this substrate 2 isapproximately 42% of the track pitch TP. After the reflection layer 3 isformed on one side of the substrate 2, the signal recording layer 4 witha thickness of approximately 200 nm is formed on the reflection layer 3and the light-transmitting layer 5 with a thickness of approximately 0.1mm is further formed on the signal recording layer 4.

[0044] According to the manufacturing method as described above, apredetermined pattern can be formed on the substrate 2 by using thestamper 30 having surface roughness (Ra) of 0.4 nm or less and therecess part 30 b with a width of not less than 30% and less than 50% ofthe track pitch. In producing this stamper 30, an existing cuttingmachine can be used as the disc master 20 is etched. The substrate 2formed by using the stamper 30 has its one side flatly formed andtherefore the reflection layer 3 which can securely reflect a light beamincident from the side of the light-transmitting layer 5 can be formedon the one side of the substrate 2. In this manufacturing method, thewidth of the land 2 a on the signal recording layer 4 can be made lessthan 50% of the track pitch TP and the optical disc 1 which can bereproduced in a reproducing device for a reproduction-only optical disccan be manufactured.

[0045] In the method for manufacturing the optical disc I according tothe present invention, the surface of the substrate 2 can be flattenedby etching one side of the disc master 20. The surface of the stamper 30for forming the land 2 a and the groove 2 b on the substrate 2 hassurface roughness (Ra) of 0.6 to 0.8 nm when the surface of the discmaster 20 is not etched. However, the surface roughness of the stamper30 is reduced to 0.4 nm or less by etching. As a result, in thismanufacturing method, the surface of the substrate 2 can be flatlyformed and the recording/reproducing characteristic of the optical disc1 can be improved. For example, in the case of an optical discmanufactured by using a stamper which is manufactured without etchingthe surface of the disc master 20, C/N of an 8T signal with a lineardensity of 0.13 μm/bit is 54 dB, whereas in the case of the optical disc1 manufactured by using the stamper 30 manufactured on the basis of thedisc master 20 which is etched once, this C/N can be improved to 56 dB.Moreover, in the case of the optical disc 1 manufactured on the basis ofthe disc master 20 which is etched twice, C/N can be improved to 59 dB.

[0046] The above-described manufacturing method can also be applied to amethod for manufacturing a reproduction-only optical disc, that is, anoptical disc such that a pit string corresponding to recording signalsis formed on one side of the substrate 2. For example, in the case wherea reproduction-only optical disc is manufactured by using a light beamwith a wavelength of 266 nm in accordance with the above-describedmanufacturing method, the jitter is 14% or more when etching of the discmaster 20 is not carried out, but the jitter can be improved to 9.6% byetching the disc master 20 only once. This etching reduces the width ofthe land 2 a formed on the substrate 2, and when this etching is carriedout on the stamper 30, the thickness of the land 2 a which is reducedtoo much can be restored to a predetermined width, thus reducing defectsof the stamper 30. The etching carried out on the stamper 30 caneliminate minute recesses and protrusions generated on the surface whenmanufacturing the stamper 30 and therefore it can flatten the surface ofthe substrate 2 to be molded.

[0047] As described above, in the present invention, the number of timesof etching carried out on the disc master 20 is not limited to theabove-described examples and can be changed in accordance with theperformance of the etching device, the surface roughness (Ra) of thestamper 30 and the width of the recess part 30 b of the stamper 30. Asdescribed above, the present invention can be applied not only to therecordable optical disc 1 but also to a reproduction-only optical disc.

[0048] Industrial Applicability

[0049] Since the stamper for optical disc according to the presentinvention has surface roughness (Ra) of 0.4 nm or less, the surface ofthe substrate to which a recess/protrusion pattern is transferred can bemade flatter than in the conventional technique. Moreover, thereflection layer provided on the substrate can be flatly provided. Thus,as a light beam is reflected by the reflection layer without causingdiffuse reflection, the optical disc having an excellentrecording/reproducing characteristic can be manufactured.

[0050] In the method for manufacturing an optical disc according to thepresent invention, since the surface is flattened by etching the discmaster, the stamper having the above-described surface roughness (Ra) of0.4 nm or less can be manufactured irrespective of the wavelength of alight beam of a cutting machine.

[0051] Moreover, since the substrate of the optical disc according tothe present invention is formed by the stamper having surface roughness(Ra) of 0.4 nm or less, the reflection layer is flatly provided andtherefore can securely reflect a light beam, thus improving therecording/reproducing characteristic.

1. A stamper for optical disc having a recess/protrusion pattern formedon one side thereof, the recess/protrusion pattern being fortransferring a predetermined pattern to a substrate of an optical disc,said one side having surface roughness (Ra) of 0.4 nm or less.
 2. Thestamper for optical disc as claimed in claim 1, wherein a recess partconstituting the recess/protrusion pattern provided on said one side hasa width of not less than 30% and less than 50% of a track pitch.
 3. Thestamper for optical disc as claimed in claim 1, wherein the track pitchis 0.35 μm or less.
 4. The stamper for optical disc as claimed in claim1, wherein said recess/protrusion pattern is provided in a signalrecording area and at least in one of non-signal recording areas on aninner circumferential side and an outer circumferential side.
 5. Amethod for manufacturing an optical disc comprising: a step of applyinga photoresist to a substrate, exposing and developing the photoresist toform a recess/protrusion pattern on one side, and forming a disc masteron which a transfer pattern is formed on the basis of the substrate; astep of etching one side of said disc master and thus reducing the widthof a protruding part constituting said transfer pattern; a step offurther transferring the transfer pattern of the disc master with thereduced width of said protruding part and thus forming a stamper; and astep of transferring the recess/protrusion pattern provided on saidstamper and thus forming a predetermined pattern on a substrate of anoptical disc.
 6. The method for manufacturing an optical disc as claimedin claim 5, wherein the side of said stamper where the recess/protrusionpattern is formed has surface roughness (Ra) of 0.4 nm or less.
 7. Themethod for manufacturing an optical disc as claimed in claim 5, whereina recess part constituting the recess/protrusion pattern of said stamperhas a width of not less than 30% and less than 50% of a track pitch. 8.The method for manufacturing an optical disc as claimed in claim 5,wherein said stamper has a track pitch of 0.35 μm or less.
 9. The methodfor manufacturing an optical disc as claimed in claim 5, wherein saidphotoresist is applied to a thickness of 30 nm or less on saidsubstrate, and said exposure is carried out by using a laser beam with awavelength of 257 nm or more.
 10. An optical disc comprising areflection layer and a protection layer stacked on a substrate which hasa predetermined recess/protrusion pattern provided on one side thereof,said substrate having said predetermined pattern formed thereon as arecess/protrusion pattern is transferred thereto by a stamper havingsurface roughness (Ra) of 0.4 nm or less.
 11. The optical disc asclaimed in claim 10, wherein a recess part constituting therecess/protrusion pattern of said stamper has a width of not less than30% and less than 50% of a track pitch.
 12. The optical disc as claimedin claim 10, wherein said stamper has a track pitch of 0.35 μm or less.13. The optical disc as claimed in claim 10, wherein therecess/protrusion pattern of said stamper is provided in a signalrecording area and at least in one of non-signal recording areas on aninner circumferential side and an outer circumferential side.
 14. Theoptical disc as claimed in claim 10, wherein a signal recording layer isprovided between said reflection layer and said protection layer. 15.The optical disc as claimed in claim 10, wherein said protection layerhas light transmittancy.